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肌肉疲劳的惊人原因-克里斯汀•莫罗 – 译学馆
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肌肉疲劳的惊人原因-克里斯汀•莫罗

The surprising reason our muscles get tired - Christian Moro

“温斯顿累得像摊浆糊”——乔治•奥威尔《1984》
你正在举重
You’re lifting weights.
第一下感觉很轻松
The first time feels easy,
但之后每举一下你就会觉得越来越费力
but each lift takes more and more effort
直到无法再举起来
until you can’t continue.
在你的手臂里
Inside your arms,
负责举重的肌肉变得无法收缩
the muscles responsible for the lifting have become unable to contract.
为什么我们的肌肉会疲劳?
Why do our muscles get fatigued?
我们经常责怪乳酸或是我们把精力用光了
We often blame lactic acidor running out of energy,
但这些因素本身并不能解释肌肉疲劳
but these factors alone don’t accountfor muscle fatigue.
还有另一个重要的原因:
There’s another major contributor:
肌肉对大脑信号的反应能力
the muscle’s ability to respondto signals from the brain.
要了解肌肉疲劳的根源
To understand the roots of muscle fatigue,
最好先了解下肌肉
it helps to know how a muscle contracts
如何接受神经的信号并做出收缩的回应
in response to a signal from a nerve.
这类信号会在几分之一秒内
These signals travel from the brain to the muscles
由大脑经长而细的运动神经元
in a fraction of a second
传送到肌肉
via long, thin cells called motor neurons.
运动神经元与肌肉细胞之间
The motor neuron and the muscle cell
有个微小的间隙
are separated by a tiny gap,
并且透过这个间隙进行的粒子交换使肌肉收缩
and the exchange of particlesacross this gap enables the contraction.
在间隙的一侧
On one side of the gap,
运动神经元含有一种称为乙酰胆碱的神经物质
the motor neuron contains a neurotransmitter called acetylcholine.
在另一侧 带电的粒子或离子
On the other side, charged particles, or ions,
排列在肌肉细胞薄膜上:
line the muscle cell’s membrane:
钾离子在内部 钠离子在外部
potassium on the inside,and sodium on the outside.
为了响应来自大脑的信号
In response to a signal from the brain,
运动神经元释放出乙酰胆碱
the motor neuron releases acetylcholine,
促使肌肉细胞膜上的孔洞打开
which triggers pores on the musclecell membrane to open.
钠离子向内流动 钾离子向外流动
Sodium flows in, and potassium flows out.
这些电荷粒子的流动是肌肉收缩的重要步骤:
The flux of these charged particles is a crucial step for muscle contraction:
电荷的变化产生一种电波信号
the change in charge creates an electrical signal
叫作动作电位
called an action potential
它会穿过肌肉细胞
that spreads through the muscle cell,
同时释放储存在内部的钙离子
stimulating the release of calciumthat’s stored inside it.
如此大量的钙离子导致肌肉收缩
This flood of calcium causesthe muscle to contract
使储存在肌肉纤维中的蛋白质锁在一起
by enabling proteins buried in the musclefibers to lock together
并互相咬合将肌肉拉紧
and ratchet towards each other, pulling the muscle tight.
用来驱动收缩的能量来自称为三磷酸腺苷的分子(简称ATP)
The energy used to power the contraction comes from a molecule called ATP.
之后三磷酸腺苷也有助于将离子从薄膜打回去
ATP also helps pump the ions backacross the membrane afterward,
让钠离子与钾离子回到两侧重新排列
resetting the balance of sodiumand potassium on either side.
每次肌肉收缩时都会重复整个过程
This whole process repeatsevery time a muscle contracts.
随着每一次收缩
With each contraction,
三磷酸腺苷的能量会消耗殆尽
energy in the form of ATP gets used up,
像乳酸这样的代谢废物会产生
waste products like lacticacid are generated,
一些离子从肌肉的细胞薄膜散去
and some ions drift away from the muscle’scell membrane,
留下越来越小的离子群
leaving a smaller andsmaller group behind.
虽然肌肉细胞反复收缩会消耗三磷酸腺苷
Though muscle cells use up ATP as theycontract repeatedly,
但它们仍会产生更多
they are always making more,
所以大多数时候 即使肌肉疲惫不堪
so most of the time even heavily fatigued muscles
也没有耗尽这一能量源
still have not depleted this energy source.
而且虽然许多代谢废物都是酸性的
And though many waste products are acidic,
疲劳的肌肉仍旧使酸碱保持在正常范围内
fatigued muscles still maintain pHwithin normal limits,
表明组织正有效地清除这些废物
indicating that the tissue is effectivelyclearing these wastes.
但最终 在这些重复收缩的过程中
But eventually, over the course ofrepeated contractions
可能没有足够浓度的钾离子
there may not be sufficient concentrations of potassium,
钠离子和钙离子
sodium or calcium ions
能让肌肉细胞薄膜
immediately available nearthe muscle cell membrane
立即适当地重置系统
to reset the system properly.
所以即使大脑传递一个信号
So even if the brain sends a signal,
肌肉细胞也无法产生收缩所需要的动作电位
the muscle cell can’t generate the actionpotential necessary to contract.
即使肌肉细胞中或周围的钠离子
Even when ions like sodium,potassium or calcium
钾离子或钙离子被耗尽
are depleted in or around the muscle cell,
这些离子在身体的其他部位也非常丰富
these ions are plentifulelsewhere in the body.
在很短的时间内
With a little time,
它们会流回需要它们的部位
they will flow back to the areas where they’re needed,
有时候会有活跃的钠离子与钾离子的帮助
sometimes with the help of active sodiumand potassium pumps.
所以如果你停下来歇会儿
So if you pause and rest,
这些离子会重新充满整个肌肉 疲劳感就会消退
muscle fatigue will subside as these ions replenish throughout the muscle.
你运动的越有规律
The more regularly you exercise,
肌肉就越不容易疲劳
the longer it takes for muscle fatigue to set in each time.
那是因为你越强壮
That’s because the stronger you are,
大脑到肌肉收缩的神经信号 循环次数就越少
the fewer times this cycle of nerve signal from the brain to contraction in the muscle
要重复举起一定的重量(才会疲劳)
has to be repeated to lift a certain amount of weight.
较少的循环代表较慢的离子消耗
Fewer cycles means slower ion depletion,
所以当你的体能提高时
so as your physical fitness improves,
你就能在相同强度下 锻炼更长的时间
you can exercise for longerat the same intensity.
许多肌肉都在运动中成长
Many muscles grow with exercise,
而且更大的肌肉也会储存更多的三磷酸腺苷
and larger muscles alsohave bigger stores of ATP
清除代谢废物的能力也更强
and a higher capacity to clear waste,
未来锻炼更长的时间才会感到疲劳
pushing fatigue evenfarther into the future.
现在 在视频中找出让你的肌肉变得更大更强的方法吧
Now, find out how to make your muscles bigger and stronger in this video.

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视频概述

举重时,第一下感觉会很轻松 但随后每举一下,就要花更多的力气,直达无法再举起。在你的手臂里,负责举重的肌肉无法再收缩了。这样的情况是如何发生的呢?克里斯汀•莫罗向我们解释了肌肉的伸缩原理,以及造成它们疲劳的原因。

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翻译译者

甪里

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视频来源

https://www.youtube.com/watch?v=rLsimrBoYXc

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